Non-destructive surface testing goes 50 nm deep

In a world first, a team of French and Danish researchers from Leti and STMicroelectronics successfully performed non-destructive testing on a CMOS stack layer embedded at a depth of more than 50 nm, locating it to within 10% accuracy.
The team, working at ESRF, used X-ray photoelectron spectroscopy—a method until now used exclusively for extreme surface testing (depths of less than 10 nm). The researchers combined their method with a quantitative signal processing algorithm for energy losses; the algorithm could potentially be used in a clean room for testing closer to the surface.

A generic, non-invasive method
This breakthrough opens new doors for the characterization of nanocomponents. These components typically contain stacked layers, and engineers need to be able to check the layers’ interface quality and depth after fabrication. Engineers also need to be able to measure the depth diffusion of ultra-thin layers.
The new X-ray photoelectron spectroscopy method can do all of the above, with three major advantages: it is non-destructive; it is non-invasive (the materials are not altered); and it does not require any sample preparation. Moreover, it can be used on a wide range of components like CMOS III-V, transistors, and memory.
The method was initially used to analyze 56-nm-deep layers in CMOS stacks made by STMicroelectronics. Now researchers are working to enhance the method, which can probably reach depths of up to 100 nm.

Contact: olivier.renault@cea.fr

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